Optical networks are the subject of increasing interest in telecommunications primarily due to their immense information handling capacity. One of the key elements of such a network is the wavelength tunable laser which allows the emission of several wavelengths from a single laser, and thereby provides multiple channels for transmission. In at least one form of the laser, light from the backface of the laser is used to lock the laser light onto the desired wavelengths.
In many types of present optical assemblies, the laser is mounted on a substrate, which is usually silicon, along with a lens near the front face, and a photodetector near the back face. A channel is used to reflect light from the back face onto the photodetector for monitoring the back face light. (See, e.g., U.S. Pat. No. 5,881,193 issued to Anigbo, which is incorporated by reference herein.) A problem arises when the same type of substrate is used in an assembly where the back face light is employed for locking the light emission wavelength, as opposed to simply monitoring the back face light intensity. A photodetctor array used for locking is placed adjacent to the channel, and receives both direct light from the back face and reflected light from the channel. The secondary “beamlets” can corrupt the wavelength monitoring signal, which reduces the ability to lock the output wavelength of the laser. A different type of substrate might be employed, but it is more economical for most manufacturers to continue using the same type of substrate used for other devices.
It is desirable, therefore, to provide an assembly which increases the quality of the detected back face light for locking the wavelength of the emitted light and for other uses.